Stimulation of the Water Transport in the Jejunum of the Rat by Ethyl Acetate

The transport of water across epithelial layers is coupled with the transport of solutes (1-3). If an isosmotic solution is placed into the lumen of the intestine, net water transport or water absorption occurs as a consequence of a net solute transport. The solute primarily involved in the transport of water is the sodium ion which is actively transported into the intercellular spaces, causing these to become hyperosmotic; consequently, water is drawn osmotically into these spaces and then transferred into the serosal compartment or into the circulation. Such “local osmosis” has been demonstrated in various epithelial cells (4) and recently also in the rectal pads of insects (5). The sodium transport, which is responsible for most of the net water transport, is an active energy-requiring process. In vivo measurements in human indicated that the ileum is capable of net water absorption against some 10 times higher salt concentration gradient than the jejunum (6). A less striking topographic difference was recorded in the rat intestine in vitro (7). In the absence of a source of energy, the rat small intestine suspended in an isosmotic medium in vitro transports little water. On the other hand, if glucose is added to the medium the sodium and water transport is greatly stimulated (8). Surprisingly, in the rat jejunum, intermediates of glucose metabolism, such as pyruvate or acetate, cannot stimulate the sodium and water absorption (9). These findings spurred speculation whether the metabolism of glucose in the intestinal epithelium is perhaps different from that in other tissues. Alternatively, it could be assumed that the pyruvate or acetate ions, because they are mostly ionized at the pH of the tissues, cannot enter the epithelial cells, while glucose passes readily across the cell membrane with the help of the specific carrier.